The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A thermocouple is a sensor used to measure temperature. Thermocouples generally include two wires made from dissimilar materials. The wires are welded together at one end, creating a junction. When a junction experiences a change in temperature, a voltage is created. This voltage, in turn, can then be interpreted to calculate the temperature at the junction point.
There are generally three types of thermocouples used when measuring temperature—exposed thermocouples, grounded thermocouples, and ungrounded thermocouples. An exposed thermocouple has junction outside the probe wall or sheath and is therefore directly exposed to the target medium. These types of thermocouples have excellent heat transfer and quick response times but are limited by the type of target media when they can be used. Generally, these thermocouples are not suitable for caustic or corrosive environments.
For ungrounded thermocouples, the sensing junction of this type of thermocouple is physically located within a sheath, but is electrically isolated from the sheath. This results in a slow response time, but has the advantage in that the electrical isolation provided by not being connected to the sheath gives these thermocouples more accurate measurements due to reduced noise. These thermocouples can also be used in caustic or corrosive environments and are more robust, as the sheath provides protection from the environment.
Grounded thermocouples also utilize a sheath but have the junction in direct electrical contact with the sheath. These thermocouples have a faster response time than ungrounded thermocouples and can be used in caustic or corrosive environments. However, these thermocouples are generally susceptible to electrical noise, such as ground loops, which impacts accuracy, especially when measuring small variations in temperature.